The absolute angular position of a motor vehicle steering wheel, also referred to as the steering- or rotation-angle, is, for example, required for monitoring or controlling a vehicle dynamic control system. The dynamic control system evaluates the rotation-angle and converts it to various control actuators, such as the brakes. Other typical applications which use rotation-angle as an input include, for example, torque vectoring systems, yaw control systems, chassis controlled stability enhancement systems, electrically assisted power steering, steer-by-wire systems and navigation systems.
Steering wheel position sensors are used in automotive applications for electronic monitoring of steering functions of a motor vehicle. In particular, position sensors are used for determining the angular position of a steering shaft as a user turns a steering wheel. An example of a position sensor is disclosed in U.S. Pat. No. 5,930,905 (the ″905 patent) to Zabler et al. The '905 patent discloses a gear having teeth coupled to a shaft. The teeth engage teeth disposed on a second gear and a third gear. The three gears have a different number of teeth. A pair of absolute position sensors is positioned in proximity to the second gear and the third gear for generating an output that corresponds to the angular positions of the gears. As long as the number of teeth on each of the gears is known, it is possible to calculate the angular position of the steering shaft based on the outputs of the absolute position sensors.
Although the above-mentioned position sensor assembly may be useful, it requires two fine accuracy rotary sensors, which are costly to manufacture and package (i.e., in the confines of a motor vehicle steering column). Other position sensor assemblies utilize a fine accuracy rotary sensor and a coarse sensor. However, these position sensor assemblies require the use of a mechanism that is large and cumbersome to package within the tight confines of a vehicle steering column.
In view of the above, there exists a need for an a improved, cost-efficient position sensor assembly which combines sensors to determine the angular rate as well as the absolute angular position of a motor vehicle steering wheel.